1. Field
The present invention is related to tuning an analog filter, and more specifically, to tuning an analog filter in a sigma-delta modulator.
2. Related Art
Many signals in communications are analog and narrow-band. In order to process them digitally, they need to be converted by an analog-to-digital converter (ADC). A sigma delta (ΣΔ) modulator ADC (e.g., a band pass sigma delta modulator) is particularly suited for converting narrow-band signals (e.g., narrow-band frequency signals) from analog to digital. In some sigma delta modulators with analog loop filters, integrated circuit implementations suffer from process and component value variation causing the filters to need tuning.
One way of tuning the analog loop filter is by making a second implementation of the filter (i.e., a master filter), and tuning the master filter, e.g. with a pilot tone. The filter in the modulator is then slaved off of the master filter. This is sometimes referred to as a form of background tuning, as it does not interrupt normal operation. However, not only is an additional filter needed (e.g., more area and power are lost on a chip), but the accuracy of the tuning is limited by matching of the components between the two filters.
Another way would be to take the filter out of the signal-path and tune it periodically. This is sometimes referred to as foreground tuning. However, this interrupts normal system behavior. In some application, this interruption can be prohibitive.
Therefore, what is needed is a system and method that would allow for more efficient and effective tuning of an analog filter.